RNA-binding as a new paradigm for androgen receptor-mediated prostate cancer therapeutic resistance

Project Summary Given that prostate cancer is primarily driven by androgen receptor (AR) signaling, AR-targeting therapies have been the mainstay treatment for advanced prostate cancer. However, despite the advent of second- generation potent AR-pathway inhibitors such as enzalutamide, apalutamide, and abiraterone, disease progression after AR-targeting therapies remains a major challenge. AR reactivation drives disease progression in at least 70% of cases. AR can be reactivated through multiple mechanisms, with AR gene amplification and/or overexpression being particularly common. Understanding how AR resists these therapies is crucial for devising strategies to delay or prevent progression to incurable stages. The proposed study addresses this urgent need. Our preliminary studies have uncovered a novel role for AR in enhancing splicing fidelity, extending beyond its classical transcriptional activity. We also discovered that AR possesses potent RNA-binding activity, which is not impacted by current AR-targeting therapies, including enzalutamide. The overlap between AR’s RNA and DNA targets is limited. Instead, AR binds to the transcripts of over 130 splicing factors and positively regulates the expression of many of these post-transcriptionally. This regulation is consistent with the elevated levels of these splicing factors during disease progression. We hypothesize that AR binds splicing factor (and other) pre-mRNAs to promote the expression of key splicing factors, leading to efficient splicing and expression of genes critical for prostate cancer progression and resistance to AR-targeting therapies. This hypothesis will be tested through two specific aims utilizing clinically relevant model systems and clinical datasets. Aim 1 will elucidate the impact of AR-RNA interactions in prostate cancer progression and resistance to AR-targeting therapies. Aim 2 will determine the mechanisms by which AR regulates pre-mRNA splicing. Decades of research on AR have predominantly focused on its DNA-binding activity. The outcome from this study could transform our understanding of AR’s functions and its molecular contributions to prostate cancer progression and therapeutic resistance. It could also radically change the way we think about targeting AR for effective management of prostate cancer.